In the agriculture field, the occurrence of every plant disease causes a marked decrease in the yields of crops and hence the control of the plant diseases is an indispensable means for agricultural techniques. As means for controlling the diseases, there are, for example, the control of the environment for cultivation, the growing of a disease-resistant cultivar, the control of the diseases by the application of agricultural and horticultural fungicides or bactericides, and the biological control of the diseases by the use of organic materials or the like. Of these, the control using agricultural and horticultural fungicides or bactericides is direct and the most effective. However, great dependence on a means comprising direct control of the diseases by the application of a large amount of the fungicides or bactericides is clearly undesirable because of problems such as environmental pollution and influences on environmental living things.
In such a situation, agricultural and horticultural fungicides and bactericides have been developed which are specifically effective against pathogenic fungi and bacteria, respectively, and have a very excellent fungicidal or bactericidal action from the viewpoint of selective toxicity. Such chemicals, however, are disadvantageous in that they tend to bring chemical tolerance to the pathogenic fungi or bacteria. As to a countermeasure against this problem, a plurality of chemicals different in action are applied as a mixture thereof or in rotation.
In order to solve the problem of excessive dependence on such chemical agrochemicals, methods for controlling various crop plant diseases or insect pests by utilizing microorganisms or natural enemies, which are generally present in the natural world, have come to be put to practical use in recent years and a controlling system has come to be improved. For example, patent document 1 has proposed that cells of a microorganism such as Bacillus subtilis FR-2, Bacillus polymyxa KT-8 or the like should be used as a controller for infection with plant fungi. The efficacy and kind of such a controller are not yet sufficient and a superior biological controller is required.
In order to solve the problem of the appearance of chemical-resistant fungi and bacteria, it is considered the most effective to utilize a substance or a microorganism, which can induce disease resistance in plants.
Although a certain number of substances capable of inducing disease resistance in plant, such as salicylic acid have been known before now, only some of them, such as S-methyl 1,2,3-benzothiazole-7-carboxylate (common name: Acibenzolar-S-methyl) (non-patent document 1 and non-patent document 2) and 3-(2-propyleneoxy)-1,2-benzisothiazole-1,1-dioxide (common name: Probenazole) (non-patent document 3) are actually used as chemicals for controlling plant diseases. Thus, such substances are not satisfactory.
Patent document 2 describes the impartment of resistance to plant diseases by the use of bacteria capable of inducing disease resistance in plants and an organic soil conditioner. This method, however, is not satisfactory.
On the other hand, patent document 3 has reported that an antimicrobially active substance KT-6291A (Fusaricidin A) produced by Bacillus sp. KB-291 controls various plant diseases. However, it has been revealed that the antimicrobially active substance KT-6291A described in patent document 3 is inactive not only against cucumber bacterial blight bacterium, a Gram-negative bacterium but also against other Gram-negative bacteria. Patent document 3 does not describe a method for controlling plant diseases caused by Gram-negative bacteria. In addition, it has been revealed that the substance KT-6291A has no antimicrobial activity against Fusarium wilt of cucumber fungus, a strain belonging to the genus Fusarium. Patent document 3 describes other substances having antimicrobial activity against several microorganisms but does not give any information regarding an activity of inducing disease resistance in plant.
Similarly, non-patent document 4 reveals that an antimicrobially active substance Fusaricidin A is produced by Bacillus polymyxa KT-8 but that this substance is inactive against Gram-negative bacteria.
In addition, non-patent document 5 reveals that Fusaricidin B and the like are produced together with Fusaricidin A by Bacillus polymyxa KT-8 but that these substances are also inactive against Gram-negative bacteria.    Patent document 1: JP-A-6-253827    Patent document 2: JP-T-2003-529539    Patent document 3: JP-A-2-275898    Non-patent document 1: Plant Physiol. 117, p. 1333-1339 (1998)    Non-patent document 2: Brighton crop protection conference—pest & diseases—1996, 8A-4, CGA2455704    Non-patent document 3: Annu. Rev. Phytopathol. 32, p. 439-59, (1994)    Non-patent document 4: The Journal of Antibiotics VOL. 49, No. 2, p. 129-135 (1996)    Non-patent document 5: The Journal of Antibiotics VOL. 50, No. 3, p. 220-228 (1997)